Two Democratic Congressman released several emails, which they claim show that Mike Duke, chief executive of the giant retailer, and other senior executives were aware of allegations the company had paid bribes to secure planning permission for a store in Teotihuacan, near Mexico City.

“It would be a serious matter if the chief executive of one of our nation’s largest companies failed to address allegations of a bribery scheme,” Congressmen Henry Waxman and Elijah Cummings wrote in a letter to Mr Duke.

The claims put pressure on Wal-Mart, which is already investigating allegations that its Mexican arm paid $24m (£15m) of bribes to accelerate its expansion in the country.

The Securities and Exchange Commission and the Department of Justice are also investigating the allegations, which first came to light in a New York Times report last year.

“This information has been part of the company’s ongoing investigation of potential violations of the Foreign Corrupt Practices Act [FCPA] for more than a year,” Wal-Mart said in response to the letter and emails.

Mr Cummings and Mr Waxman claim the emails contradict Wal-Mart’s statement last month that Mr Duke and other executives were aware of local opposition to the planned store in Teotihuacan, but did not know of allegations of bribery.

A spokesman for Wal-Mart said the Congressmen’s letter “leaves the wrong impression that our public statements are contradicted by the information they released”.

Alongside the release of its third-quarter results in November, Wal-Mart warned that US authorities’ investigation into possible violations of the FCPA had expanded beyond Mexico. The controversy is a blow to Wal-Mart, which has tried over the past decade to overhaul a corporate image dented by concerns about its labour practices.

Wal-Mart said it wanted to provide the Congressmen with “whatever appropriate information we can to help them and we have already provided committee staff with multiple briefings”.

Shares in Wal-Mart fell 0.3pc to $68.36 in early trading on Wall Street.